1. Field of the Invention
The present invention relates to a liquid-jet head that ejects jets of liquid and to a liquid-jet apparatus. More particularly, the present invention relates to an ink-jet recording head that pressurizes, by piezoelectric elements, ink supplied to pressure generating chambers communicating with nozzle orifices that eject ink droplets to eject the ink droplets from the nozzle orifices, and relates to an ink-jet recording apparatus.
2. Description of the Related Art
Two types of heads are put into practical use in an ink-jet recording head, in which pressure generating chambers that communicate with nozzle orifices ejecting ink droplets are partially constituted of vibration plate. The vibration plate is deformed by piezoelectric elements to pressurize ink in the pressure generating chambers, and the ink droplets are ejected from the nozzle orifices. One is a recording head using piezoelectric actuators of a longitudinal vibration mode which expand and contract in an axis direction of the piezoelectric elements, and the other is a recording head using piezoelectric actuators of a flexural vibration mode.
In the former type, a volume of each pressure generating chamber can be changed by abutting an end surface of the piezoelectric element against the vibration plate, and manufacturing of a head suitable to high density printing is made possible. On the contrary, while this is possible, it requires a difficult process of cutting and dividing the piezoelectric element in a comb tooth shape in accordance with an array pitch of the nozzle orifices and work of positioning and fixing the cut and divided piezoelectric elements to the pressure generating chambers. Thus, there is a problem of a complex manufacturing process. On the other hand, in the latter one, the piezoelectric elements can be fabricated and installed on the vibration plate by a relatively simple process of adhering a green sheet of a piezoelectric material while fitting a shape thereof to that of the pressure generating chambers and baking the green sheet. However, a certain area of the vibration plate is required due to use of the flexural vibration, thus there is a problem that a high density array of the piezoelectric elements is difficult.
Meanwhile, in order to solve such a disadvantage of the latter recording head, a recording head is proposed, in which an even piezoelectric material layer is formed over the entire surface of a vibration plate by a deposition technology, the piezoelectric material layer is cut and divided into a shape corresponding to that of pressure generating chambers by a lithography method, and piezoelectric elements are formed so as to be independent of each other for each pressure generating chamber (refer to, for example, Japanese Patent Laid-Open No. Hei 5(1993)-286131).
Accordingly, the work of adhering the piezoelectric elements to the vibration plate is eliminated, and there are advantages in that not only can the piezoelectric elements be fabricated and installed by a precise and simple method that is the lithography method but also the thickness of each piezoelectric element can be thinned to enable a high-speed drive.
However, in the ink-jet recording head in which the piezoelectric elements are arrayed in high density as described above, one electrode (common electrode) is provided commonly to the plurality of piezoelectric elements. Therefore, when a large number of piezoelectric elements are driven simultaneously to eject a large number of ink droplets at one time, a voltage drop occurs and the amounts of displacement of the piezoelectric elements become unstable, causing a problem of lowering ink ejection characteristics. Moreover, a voltage, which is applied to a piezoelectric element provided on a position farther from a terminal portion to which external wiring is connected, is apt to be lowered. Therefore, there is a problem of variations in ejection characteristics of liquid droplets depending on distances from the terminal portion even in piezoelectric elements provided parallel in one row.
Although such problems as described above can be solved by thickening the thickness of the common electrode of the piezoelectric elements, a problem occurs that the amounts of displacement of the vibration plate, which is generated by the drive of the piezoelectric elements, are lowered because the common electrode generally constitutes a part of the vibration plate. Although the problems as described above can be solved also by expanding the area of the common electrode, there is a problem that the head is enlarged. Moreover, an electrode of a piezoelectric element formed of a thin film has a relatively high resistance value because a film thickness thereof is thin, and therefore, the problems as described above are particularly apt to occur therein.
As another means for solving the problems as described above, there is a recording head, in which a plurality of lower electrode films (lower electrodes) are divided into several groups and each common terminal is provided so as to correspond to each of the groups, thus controlling the voltage drop in attempt to equalize the properties of actuators (piezoelectric elements) (refer to, for example, Japanese Patent Laid-Open No. 2002-11877).
With such a structure, the occurrences of voltage drop are able to be controlled; however, the number of terminals is increased to such a great extent that the wiring structure becomes complicated. Therefore, there are problems that the manufacturing process becomes complicated and that it is difficult to adopt the structure when the piezoelectric element is arrayed in high density. Note that such problems needless to say exist in the manufacturing method of other liquid-jet heads that eject something other than ink, similarly to the manufacturing method of an ink-jet recording head that ejects ink.
In consideration of such circumstances as described above, it is an object of the present invention to provide a liquid-jet head that is capable of maintaining the ejection characteristics of the liquid droplets, obtaining stable ejection characteristics and arraying the piezoelectric elements in high density, and to provide a liquid-jet apparatus.
A first aspect of the present invention that attains the foregoing object is a liquid-jet head comprising: a passage-forming substrate in which pressure generating chambers communicating with nozzle orifices are formed; and piezoelectric elements for generating pressure changes in the pressure generating chambers, the piezoelectric elements being provided on one surface side of the passage-forming substrate with vibration plate interposed therebetween, characterized in that a resistance reduction portion is provided to reduce a resistance of a common electrode common to the plurality of piezoelectric elements when a voltage is applied to the piezoelectric elements, the resistance reduction portion including; common lead electrodes extracted from portions of the common electrode, the portions excluding both end portions in a direction where the piezoelectric elements are provided parallel, to outside regions opposite with the pressure generating chambers; and connection wiring composed of a bonding wire.
In the first aspect, the resistance value of the common electrode when a voltage is applied to the piezoelectric elements is substantially lowered by the resistance reduction portion. Therefore, the voltage drop can be prevented from being generated when the plurality of piezoelectric elements are driven simultaneously. Accordingly, the ejection characteristics of liquid droplets are stabilized without being varied. Moreover, the common lead electrodes are connected to one another by a connection wiring composed of a bonding wire, and thus the head is not enlarged, and the piezoelectric elements can be arrayed in high density relatively easily.
A second aspect of the present invention is the liquid-jet head according to the first aspect, characterized in that the plurality of common lead electrodes are extracted from the common electrode, and the common lead electrodes are connected to one another by the connection wiring.
In the second aspect, the occurrence of the voltage drop can be prevented more assuredly, and the variations in ejection characteristics for each of the nozzle orifices can be prevented with certainty.
A third aspect of the present invention is the liquid-jet head according to anyone of the first and second aspects, further comprising: a sealing plate joined to the piezoelectric element side of the passage-forming substrate, the sealing plate having a piezoelectric element holding portion to seal the piezoelectric element, characterized in that an exposed portion into which surfaces of the common lead electrodes are exposed is provided in a part of the sealing plate, and the connection wiring is provided in the exposed portion.
In the third aspect, the common lead electrodes can be connected, to one another even if the area of the exposed portion is relatively small, and the head can be miniaturized with certainty.
A fourth aspect of the present invention is the liquid-jet head according to any one of the first to third aspects, characterized in that the connection wiring is extended in a direction approximately perpendicular to a direction where the common lead electrodes are provided parallel.
In the fourth aspect, the common lead electrodes can be connected securely to one another in a relatively small region, and the head can be miniaturized with certainty.
A fifth aspect of the present invention is the liquid-jet head according to the third aspect, further comprising: an auxiliary wiring layer made of a conductive material on the sealing plate, characterized in that the auxiliary wiring layer is electrically connected to the common electrode and the common lead electrodes in a region corresponding to an outside of a row of the pressure generating chambers by the connection wiring extended through the exposed portion to constitute a part of the resistance reduction portion.
In the fifth aspect, the resistance value of-the common electrode is further lowered by providing the auxiliary wiring layer, therefore when the plurality of piezoelectric elements are driven, the voltage drop can be prevented more assuredly.
A sixth aspect of the present invention is the liquid-jet head according to the third aspect, characterized in that a drive IC is provided on the upper surface of the sealing plate, a conductive portion is provided on the drive IC, and the conductive portion is electrically connected to the common lead electrodes by the connection wiring to constitute a part of the resistance reduction portion.
In the sixth aspect, the resistance value of the common electrode can be substantially lowered, and the voltage drop does not occur even if a large number of the piezoelectric elements are driven simultaneously, therefore, the ejection characteristics are stabilized. Moreover, the head is not enlarged because the common lead electrodes are made conductive to one another through the conductive portion on the drive IC.
A seventh aspect of the present invention is the liquid-jet head according to the sixth aspect, characterized in that the conductive portion includes a plurality of conductive layers provided intermittingly in an island shape on the drive IC and coupling wiring composed of bonding wires, the coupling wiring electrically connecting the conductive layers to one another.
In the seventh aspect, the plurality of common lead electrodes can be made mutually conductive easily and securely, and the resistance value of the common electrode can be lowered assuredly.
An eighth aspect of the present invention is the liquid-jet head according to the sixth aspect, characterized in that the conductive portion is a conductive layer provided continuously on the drive IC across the direction where the piezoelectric elements are provided parallel.
In the eighth aspect, the plurality of common lead electrodes can be made mutually conductive easily and securely, and the resistance value of the common electrode can be lowered assuredly.
A ninth aspect of the present invention is the liquid-jet head according to any one of the first to eighth aspects, characterized in that the common lead electrodes are composed of a same layer as that of the common electrode.
In the ninth aspect, the common lead electrodes can be formed simultaneously when the common electrode is formed, and the manufacturing process can be simplified.
A tenth aspect of the present invention is the liquid-jet head according to any one of the first to eighth aspects, characterized in that the common lead electrodes are composed of a same layer as that of individual lead electrodes extracted from individual electrodes of the piezoelectric elements.
In the tenth aspect, the resistance value of the common electrode can be lowered more effectively. Moreover, the manufacturing process is simplified because the common lead electrodes can be formed simultaneously when the individual lead electrodes are formed.
An eleventh aspect of the present invention is the liquid-jet head according to any one of the first to tenth aspects, characterized in that the common lead electrodes are extended in a same direction as a direction where individual lead electrodes extracted from individual electrodes of the piezoelectric elements are extended.
In the eleventh aspect, the plurality of common lead electrodes can be extended easily without enlarging the head.
A twelfth aspect of the present invention is the liquid-jet head according to any one of the first to tenth aspects, characterized in that the common lead electrodes are extended in a direction contrary to a direction where individual lead electrodes extracted from individual electrodes of the piezoelectric elements are extended.
In the twelfth aspect, it is possible to secure a relatively wide space for forming the common lead electrodes and the connection wiring therein, and the common lead electrodes and the connection wiring can be formed relatively easily.
A thirteenth aspect of the present invention is the liquid-jet head according to any one of the first to twelfth aspects, characterized in that at least three of the common lead electrodes are provided at an approximately constant interval.
In the thirteenth aspect, the variations in voltage to be applied to the piezoelectric elements can be controlled even if a large number of the piezoelectric elements are driven simultaneously to cause the voltage drop,
A fourteenth aspect of the present invention is the liquid-jet head according to any one of the first to thirteenth aspects, characterized in that two rows of the pressure generating chambers formed by a plurality of compartment walls in the passage-forming substrate are provided, and the common lead electrodes are extended to a region corresponding to a space between the rows of the pressure generating chambers.
In the fourteenth aspect, the head can be miniaturized with more certainty because the common lead electrodes can be extended effectively from the common electrode in the regions corresponding to the two rows of the pressure generating chambers.
A fifteenth aspect of the present invention is the liquid-jet head according to any one of the first to fourteenth aspects, characterized in that the pressure generating chambers are formed in a single crystal silicon substrate by anisotropic etching, and respective layers of the piezoelectric elements are formed by deposition and lithography methods.
In the fifteenth aspect, the liquid-jet heads having high-density nozzle orifices can be manufactured relatively easily in a large quantity.
A sixteenth aspect of the present invention is a liquid-jet apparatus comprising the liquid-jet head according to any one of the first to fifteenth aspects.
In the sixteenth aspect, a liquid-jet apparatus can be realized, in which the ejection characteristics of liquid droplets are stabilized, and thus reliability is improved.